Chapter 173-423 WAC – Clean Vehicles Program

Ecology is proposing revisions to chapter 173-423 WAC, Washington’s Clean Vehicles Program rule. These revisions align with California’s changes to vehicle emissions standards that apply to new passenger and commercial vehicles sold in Washington.  

Vehicle emissions standards are an essential policy tool for addressing climate change and reducing harmful air pollution from vehicles, particularly in communities most exposed to this type of pollution. This rulemaking creates a path for reinstating older standards if current standards become unenforceable due to recent federal actions. Washington holds these recent federal actions as unlawful, and litigation is ongoing. The older standards that this rulemaking would reinstate were phased out in favor of the current, more protective standards. However, they are still a safer and more effective fallback than the federal standards Washington would default to without these rule changes.  

Ecology is proposing to adopt amendments to Advanced Clean Cars and Advanced Clean Cars II, both of which apply to light-duty passenger vehicles, pickup trucks, and medium-duty vehicles. Amendments would re-establish Advanced Clean Cars certification standards for combustion engine vehicles—which were replaced by Advanced Clean Cars II beginning in model year 2026—as a certification option for manufacturers. These certification standards ensure that new combustion engine vehicles sold in Washington pollute less.   

Additionally, Ecology is proposing to adopt components of California’s 2010 medium- and heavy-duty vehicle in-use standards, which were replaced by Heavy-Duty Low NOx Omnibus. Similar to the light-duty standards above, the 2010 in-use regulation would act as a backstop emission standard for medium- and heavy-duty vehicles if the federal government successfully eliminates our ability to enforce Heavy-Duty Low NOx Omnibus. 

California Regulations Proposed for Adoption by Reference: 

The relevant sections that Ecology is considering adopting by reference from the California Code of Regulations are listed below.  

Revising Existing Sections: 

• California Code of Regulations, Title 13  
• 1900, 1956.8, 1961.2 – 1961.4, 1962.2 – 1962.4, 1965, 1968.2, 1968.5, 1969, 1971.1, 1971.5, 1976, 1978, 2035 – 2038, 2040, 2111 – 2119, 2121, 2123, 2125 – 2131, 2137, 2139 – 2149 (including 2139.5), 2166, 2166.1, 2167, 2168, 2169, 2169.1- 2169.8, 2170, 2423, 2485
• California Code of Regulations, Title 17 
• 95300 – 95307, 95311, 95660 – 95663 

New Sections: 

• California Code of Regulations, Title 13  
• 1900.0.1,1956.8.1, 1956.8.2, 1961.2.1, 1962.2.1, 1962.3.1, 1965.0.1, 1968.2.1, 1968.5.1, 1969.0.1, 1971.1.1, 1971.5.1, 1976.0.1, 1978.0.1, 2035.0.1 – 2040.0.1, 2111.0.1 – 2119.0.1, 2121.0.1, 2123.0.1, 2125.0.1 – 2131.0.1, 2137.0.1, 2139.0.1 – 2149.0.1, 2317.0.1, 2423.0.1, 2485.0.1
• California Code of Regulations, Title 17 
• 95300.0.1 – 95307.0.1, 95311.0.1, 95660.0.1 – 95663.0.1 

Ecology is also proposing additional fleet reporting requirements, beyond the one-time report required in 2023, to authorize additional data collection. This data would be used to support utility grid planning, the development of state-funded transportation electrification grant programs, and other efforts to reduce carbon emissions from transportation. 

These rule revisions are important to streamline program implementation, provide additional compliance flexibility and clarity, maintain consistency with other states and the federal government, and work toward meeting Washington’s limits on greenhouse gas emissions. 

Current Clean Vehicle Regulations Overview  

The Advanced Clean Cars and Advanced Clean Cars II regulations apply to light-duty passenger vehicles, pickup trucks, and medium-duty vehicles. They include two major standards: more stringent engine emission requirements, and sales targets that require zero-emission models to make up an increasing percentage of new vehicle sales in WA, starting with model year 2025. 

California’s 2010 medium- and heavy-duty vehicle in-use standards and the Heavy-Duty Low-NOx Omnibus regulation both apply to heavy-duty internal combustion engine manufacturers and require them to meet more protective air quality standards. Omnibus raises the stringency of requirements initially established under the 2010 medium- and heavy-duty vehicle in-use standards and covers subsequent model years to the 2010 standards.  

The 2023 one-time fleet reporting requirement obligated fleets of 5 or more medium- or heavy-duty vehicles, or over $50 million in annual revenue, to report on their 2022 vehicle operations. These reports included such data as number and age of vehicles, operating characteristics such as miles traveled and fuel type used, and the locations where the vehicles were housed (e.g., fleet depot).